Interstitial Lung Diseases

ILD Overview - The Lung Labyrinth

• Definition: Diverse group of diffuse parenchymal lung diseases affecting the interstitium, causing inflammation and/or fibrosis.
• Key Symptoms: Progressive exertional dyspnea, persistent dry cough.
• Key Sign: Bibasilar fine inspiratory crackles ('Velcro rales'). Clubbing possible.
• Basic Pathophysiology: Alveolitis → Chronic Inflammation → Fibrosis → Impaired gas exchange, stiff lungs.
• PFTs: Restrictive pattern: ↓TLC, ↓DLCO; normal or ↑ $FEV_1/FVC$ ratio.
• Broad Classification:
  • Known causes: Drugs (amiodarone, bleomycin), CTD (RA, SSc), environmental (asbestosis, silicosis).
  • Idiopathic Interstitial Pneumonias (IIPs): e.g., IPF, NSIP.
  • Granulomatous: Sarcoidosis, Hypersensitivity Pneumonitis (HP).
  • Rare ILDs.

⭐ Bibasilar 'Velcro' crackles are a characteristic auscultatory finding in many ILDs, especially IPF.

IPF - Scarred Scenery

• Most common, severe Idiopathic Interstitial Pneumonia (IIP).
• Affects older adults (>60 yrs), M>F predominance.
• Pathology: Usual Interstitial Pneumonia (UIP) pattern (hallmark: spatial & temporal heterogeneity).
• HRCT Chest (essential for diagnosis):
  • Bilateral, basal, subpleural reticulation.
  • Honeycomb cysts.
  • Traction bronchiectasis.
  • Absence of: extensive Ground Glass Opacities (GGO), nodules, consolidation.
• Diagnosis of exclusion: Rule out Connective Tissue Disease (CTD), drug toxicity, chronic Hypersensitivity Pneumonitis (HP).
• Prognosis: Poor; median survival 3-5 years.
• Management:
  • Antifibrotics: Pirfenidone, Nintedanib (slow Forced Vital Capacity (FVC) decline).
  • Supportive: O2, pulmonary rehabilitation.
  • Lung transplant.
• 
• ⭐ > The UIP pattern on HRCT, characterized by subpleural, basal predominant honeycombing, is crucial for IPF diagnosis.

Sarcoidosis - Granuloma Galaxy

• Unknown etiology multisystem disorder; hallmark: non-caseating granulomas.
• Pulmonary involvement: >90% of cases.
• CXR Staging (Scadding):

![CXR Sarcoidosis Stages I-IV](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Internal_Medicine_Pulmonology_Interstitial_Lung_Diseases/30f05fd5-1ed8-465f-a93d-c21ac9db429c.png)

• Extrapulmonary sites: Skin (erythema nodosum, lupus pernio, maculopapular rash), eyes (uveitis, conjunctivitis), lymph nodes, liver, spleen, heart, nervous system.

⭐ Löfgren's syndrome (acute arthritis, erythema nodosum, and bilateral hilar lymphadenopathy) is an acute form of sarcoidosis with a good prognosis.

• Diagnosis: Compatible clinical/radiological findings + histological evidence of non-caseating granulomas + exclusion of other granulomatous diseases.
• Lab findings: ↑ Serum Angiotensin-Converting Enzyme (ACE) (non-specific, reflects granuloma load). Hypercalcemia/hypercalciuria (due to macrophage $1\alpha$-hydroxylase activity).

Other Key ILDs - Diverse Diffusopathies

• Hypersensitivity Pneumonitis (HP): Immune reaction to inhaled organic antigens (Farmer's lung, Bird fancier's lung).
  • Acute, subacute, chronic (can → fibrosis).
  • HRCT: Acute/Subacute - centrilobular ground-glass nodules, mosaic attenuation. Chronic - fibrosis.
  • Rx: Antigen avoidance, corticosteroids.
• Connective Tissue Disease-Associated ILD (CTD-ILD): Common in Scleroderma (SSc), Rheumatoid Arthritis (RA), Polymyositis/Dermatomyositis (PM/DM).
  • Patterns: NSIP (SSc), UIP (RA-ILD, poorer prognosis), OP.
• Pneumoconioses:
  • Silicosis: Silica dust. Upper lobe nodules, Progressive Massive Fibrosis (PMF). ↑ TB risk.

    ⭐ 'Egg-shell' calcification of hilar lymph nodes on chest X-ray is highly suggestive of silicosis.

  • Asbestosis: Asbestos fibers. Lower lobe fibrosis, pleural plaques. ↑ risk of lung cancer & mesothelioma.

High‑Yield Points - ⚡ Biggest Takeaways

• IPF: UIP pattern (honeycombing, traction bronchiectasis) on HRCT; treat with Pirfenidone/Nintedanib.
• Sarcoidosis: Non-caseating granulomas, bilateral hilar lymphadenopathy, ↑ACE, hypercalcemia; Lofgren's syndrome.
• Hypersensitivity Pneumonitis: Antigen exposure (farmer's/bird fancier's lung); antigen avoidance is crucial.
• CTD-ILD: Common with scleroderma, RA; NSIP pattern is frequent.
• Pneumoconioses: Occupational dusts (silicosis: ↑TB risk; asbestosis: mesothelioma).
• ILDs show restrictive PFTs (↓TLC, ↓FVC, ↓DLCO); key drug causes: Amiodarone, Bleomycin, Methotrexate.